1. Technical Field
The present invention relates generally to a mounting structure for an EGR (Exhaust Gas Recirculation) valve for an internal combustion engine and more particularly to an improved mounting structure allowing an EGR valve to be directly installed on an intake manifold of an internal combustion engine.
2. Background Art
Recently, EGR valves for controlling the recirculation rate of exhaust gas redirected to the air intake system of internal combustion engines are frequently mounted directly on the intake manifold. A flange, for example, for installing an EGR valve is provided which is integrally formed on the intake manifold. The flange typically has internal threads. The EGR valve is mounted on the flange by tightening a bolt or a stud bolt into the internal threads.
Usually, an intake manifold for an internal combustion engine is casted of aluminum alloy and the flange for mounting the EGR valve is also made of the same material. The flange is subject to high temperatures due to the heat of exhaust gases flowing within the exhaust gas recirculation passage provided therein. This reduces the mechanical strength of the aluminum alloy. Thus, when the EGR valve is installed on the flange with bolts, the axial tension of bolts tends to cause the internal threads to deform due to continuous fatigue with the result that loosening of bolts occurs.
A water jacket provided so as to be arranged around the exhaust gas recirculation passage of the intake manifold has been proposed. However, the water jacket is adapted only for cooling exhaust gas. This water jacket, circulating a small amount of water, is not effective for cooling portions in the vicinity of the boltholes.